5Jun/093
T-SQL MERGE: My New Friend
As I was catching up on SQL 2008 this morning, I spent some time working with the T-SQL MERGE command, new in SQL 2008. Most of the blogs and examples online are a bit terse, so I decided to write a simple sample.
Check it out:
--// Create our SOURCE table DECLARE @t1 TABLE ( id int, name nvarchar(16), email nvarchar(32) ) --// Create our TARGET table DECLARE @t2 TABLE ( id int, name nvarchar(16), email nvarchar(32) ) --// Insert values into SOURCE table INSERT INTO @t1 VALUES (1, 'Charles Chen', 'charles.chen@domain.com') INSERT INTO @t1 VALUES (2, 'Sandra Chen', 'sandra.chen@domain.com') INSERT INTO @t1 VALUES (3, 'Brad Wright', 'brad.wright@domain.com') --// Insert values into TARGET table INSERT INTO @t2 VALUES (4, 'Brady Sines', 'brady.sines@domain.com') INSERT INTO @t2 VALUES (1, '', '') --// Select values from the TARGET table (just to verify) SELECT * FROM @t2 --// Merge records from source to target MERGE @t2 AS [target] USING @t1 AS [source] ON ([target].id = [source].id) WHEN NOT MATCHED BY TARGET THEN INSERT(id, name, email) VALUES([source].id, [source].name, [source].email) WHEN MATCHED THEN UPDATE SET [target].name = [source].name, [target].email = [source].email --// Get the journal of actions OUTPUT $action, inserted.*, deleted.*; --// Grab the resultant table SELECT * FROM @t2
And here are the results:
Awesome! Admittedly, I'm still trying to come up with some legitimate uses for this in my day-to-day application programming









June 7th, 2009 - 00:24
MERGE is especially useful for loading datawarehouses.
one use i’ve found fo rin normal app developemnt is the
if exists update
else insert
problem which merge solves beautifully.
June 7th, 2009 - 01:38
Yeah, that did pop up in my mind, but it seemed like it would be overkill since it would involve creating a table variable just to get it to work.
I’ve usually handled this just by doing an EXISTS first and branching (INSERT or UPDATE) depending on if the object ID already exists.
June 8th, 2009 - 09:45
yeah i did the same thing, but it has it’s problems:
http://weblogs.sqlteam.com/mladenp/archive/2007/07/30/60273.aspx
and here’s the comparison for Merge:
http://weblogs.sqlteam.com/mladenp/archive/2007/08/03/60277.aspx
and to be complete a way to get total pessimistic concurrencything out of the way.
Application Locks (or Mutexes) in SQL Server 2005:
http://weblogs.sqlteam.com/mladenp/archive/2008/01/08/Application-Locks-or-Mutexes-in-SQL-Server-2005.aspx